Boiler assembly

ABSTRACT

A boiler assembly having a unique burner box construction and a modular heat exchanger. The burner box has a primary diffuser upstream from a plurality of burners for evenly distributing a flow of air to and around the burners. The burner box also has a secondary diffuser downstream from the burners for mixing the fuel-air mixture exiting the burners with the air which flowed around the burners to create a final fuel-air mixture which can sustain stable and quiet combustion. The heat exchanger comprises a plurality of sections which define passageways for the combustion gases and circulating fluid. Reticulated ceramic cylinders are located within some of the combustion gas passageways immediately downstream of the burners to enhance heat transfer.

FIELD OF THE INVENTION

The present invention relates generally to residential and commercialsized boilers, and more particularly to a self-contained modular boilerhaving a unique burner and heat exchanger assembly which provide acompact, efficient and readily installable boiler unit having a range ofheating capacities.

BACKGROUND OF THE INVENTION

A boiler is an integral part of a heating system of a buildingstructure, or house, and is used to heat water circulating at hightemperatures through hydronic piping and radiator/convector systems. Thecirculated water is completely isolated from the outside environment.Gaseous fuels are ignited within the boiler to generate heat which istransferred to the circulating water. The spent gas is exhausted intothe atmosphere. The heated water exits the boiler, transfers the heatthroughout the building, and returns to the boiler for re-heating.

Several criteria are taken into account in the design of a boiler.Generally, the size of the boiler is in direct relation to the size ofthe space to be heated. In turn, the size of the boiler has a directrelationship on the cost of manufacture, installation, and operation ofthe boiler. Operation and maintenance costs are also affected by thethermal stresses within the boiler structure. The size of the boileralso has an effect on the building space required to house the boilerassembly.

Another design criteria is the requirement of transferring energyefficiently from the combustion gases to the circulating water.Efficient heat transfer allows the use of lower combustion temperaturesand provides lower exhaust gas temperatures. Reducing the combustiontemperature also reduces the amount of noxious emissions, such as NOxand CO.

A further design criteria is the requirement for the burner to optimizecombustion of the gaseous fuel. The burner should sustain quiet, stablecombustion so that the heated air is evenly distributed for enhancingheat exchange and fuel efficiency.

Some of these design criteria are exemplified in the boiler disclosed inU.S. Pat. No. 2,206,398 issued to Grimm. The Grimm boiler assemblyincludes a hollow front section, a hollow rear section, and one or morehollow intermediate sections which are filled with circulating water andallow the water to pass therethrough. Hot air is forced into passages inthe boiler. The hot air horizontally traverses the length of the boilerfive times before being exhausted through a flue. A plurality of heatextruders, or fins, are located along the hot gas passageways tomaximize heat transfer from the hot gases through the metal of thesections to the circulating water.

Other prior art patented boilers include U.S. Pat. No. 2,273,453 issuedto Vandenberg which discloses a boiler assembled from a plurality ofvertically aligned hollow sections. Adjacent sections are connected byhollow nipples which interconnect the water passageways between thesections. U.S. Pat. No. 4,126,105 issued to Bottcher discloses a boilerassembly comprising a plurality of horizontally aligned hollow sections.U.S. Pat. No. 5,049,324 issued to Morris et al. discloses generally theuse of reticulated ceramics as heat exchange media, and U.S. Pat. No.5,353,749 issued to Seibel et al. discloses generally the use of aseries of burners in a large industrial boiler.

Although various ones of the referenced boilers may functionsatisfactorily for their intended purposes, there is a need for a morecompact boiler assembly which tends to optimize combustion, to increaseheat transfer and to operate efficiently. The combustion process withinthe boiler should effectively operate to reduce levels of noxiousemissions exhausted to the atmosphere, and the boiler manufacturing andinstallation costs should provide savings over existing boiler designs.

OBJECTS OF THE INVENTION

With the foregoing in mind, a primary object of the present invention isto provide a novel multi-sectional and modular boiler assembly havingheat exchange sections which can readily be assembled with any number oflike sections to fit the requirements of a specific heating system.

Another object of the present invention is to provide a unique burnerassembly providing a combustion process within the boiler which isquiet, stable and burns fuel efficiently.

A further object of the present invention is to provide an improvedboiler heat exchanger which tends to optimize heat transfer so thatcombustion temperature can be reduced, noxious emissions can be reduced,and efficient use of fuel can be achieved.

SUMMARY OF THE INVENTION

More specifically, the present invention provides a boiler assembly forheating a fluid which circulates through a closed radiator/convectorheating system. The boiler assembly has a plurality of burners locatedin a path of flowing air such that air flows from an upstream directionthrough, alongside and past the burners. The burners are directed in adownstream direction and are supplied with gaseous fuel by a supplymeans.

A primary diffuser is located across the path of air upstream from theburners. The primary diffuser evenly distributes the flow of air throughand alongside the burners such that a primary fuel-air mixture iscreated inside each burner. A secondary diffuser is located across thepath of air downstream from the burners. The secondary diffuser evenlymixes the primary fuel-air mixture exiting the burners with the airwhich flowed alongside the burners to create a secondary fuel-airmixture. The secondary fuel-air mixture is ignited to sustain quiet,stable combustion downstream from the burners providing combustion gasesto heat the fluid.

In another aspect, the present invention provides a multi-section heatexchanger for transferring heat from the combustion gases to thecirculating fluid. The multi-section heat exchanger has a hollowstructure for fluid circulation and upper horizontal passageways locateddownstream from the secondary diffuser. The upper horizontal passagewaysallow the combustion gases to flow therethrough, whereby heat from thecombustion gases is transferred to the fluid through the hollowstructure by convection and radiation.

Enhanced heat transfer is accomplished by porous, sponge-like,refractory blocks located centrally in each of the upper horizontalpassageways and spaced from the walls of the upper horizontalpassageways by fin-like spacer supports. The refractory blocks provide anetwork of passages for the flowing hot combustion gases to maximizeheat transfer while minimizing pressure drop.

The multi-section heat exchanger has a rear section located downstreamfrom the upper horizontal passageways to reverse the flow of thecombustion gases downward and back toward the front of the boilerthrough lower horizontal passageways located below the upper horizontalpassageways. The lower horizontal passageways act to further transferheat from the combustion gases to the fluid by convection before beingexhausted from a location near the bottom-front of the boiler.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the presentinvention should become apparent from the following description whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is an elevational, sectional view of the inside front of a boilerassembly embodying the invention;

FIG. 2 is a right side elevational, sectional view of FIG. 1 taken online 2--2 of FIG. 1;

FIG. 2A is a perspective view of a primary diffuser, or air plateshowing its orifice pattern;

FIG. 3 is a cross-sectional view taken on line 3--3 of FIG. 2 toillustrate a front section of a heat exchanger in the boiler assembly;

FIG. 4 is a cross-sectional view taken on line 4--4 of FIG. 2 toillustrate a front section of a heat exchanger in the boiler assembly;

FIG. 5 is a cross-sectional view taken on line 5--5 of FIG. 2 toillustrate a pinned intermediate section of a heat exchanger in theboiler assembly;

FIG. 6 is a cross-sectional view taken on line 6--6 of FIG. 2 toillustrate a rear section of a heat exchanger in the boiler assembly;

FIG. 7 is a cross-sectional view taken on line 7--7 of FIG. 5 andthrough the boiler assembly to illustrate the paths of flow of thecombustion gases and the circulating fluid; and

FIG. 8 is an exploded view of the front, intermediate, pinnedintermediate, and rear sections of the heat exchanger in the boilerassembly.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a boiler 10 according to the present invention. Theboiler 10 is intended to be installed as a component of aradiator/convector heating system (not shown) which is used to heat theinterior of a commercial building or residential dwelling. A fluid, suchas water, is circulated through closed-loop piping to the boiler 10 andis received in the boiler 10 at a fluid inlet 14. The fluid is heatedwithin the boiler 10 and exits the boiler 10 at a fluid outlet 12. Theheated fluid is then circulated through the building transferring itsheat such as by baseboard radiators. The fluid is then returned to theboiler 10 for further re-heating.

To heat the fluid as it passes through the boiler 10, fuel, such as gas,is supplied to the boiler and is burned. To this end, air at ambienttemperature is drawn by a fan 18 into the boiler 10 through an air inlet16. Simultaneously, gaseous fuel is admitted to the boiler 10 throughfuel inlet 20. The air is mixed with the gaseous fuel, as will bediscussed in detail later in this application, and is ignited. The hotcombustion gases travel through boiler 10 and transfer heat to thefluid. After the heat is removed from the combustion gases, the gasesexit the boiler 10 through the flue 22 and are discharged to theatmosphere.

The boiler 10 includes a burner box 24 and a heat exchanger 26 assembledwithin a housing 28. The components and functions of the burner box 24and heat exchanger 26 are discussed in detail below.

The Burner Box

As illustrated in FIGS. 1 and 2, the burner box 24 houses a plurality ofmultiple so-called in-shot burners 30 which burn fuel to create heat.The burner box 24 is located behind a front panel 28a of the housing 28.The burner box 24 has a chamber 32 for receiving ambient air through anair supply opening 34. The chamber 32 is located between a front wall24a of the burner box 24 and a primary diffuser, or air plate, 36. Theburners 30 are positioned in the burner box 24 between the primarydiffuser 36 and a secondary diffuser, or combustion gas plate, 38. Thesecondary diffuser 38 combines with the burner box 24 which mounts tothe front section 60 to form a combustion chamber 40 adjacent the heatexchanger 26.

As illustrated in FIG. 1, the burner box 24 houses six identical burners30. Each burner 30 is tubular in shape and has an upstream end 30a and adownstream end 30b such that each burner 30 is directed toward the heatexchanger 26.

The supply of gaseous fuel to the burners 30 is regulated by an electricgas valve 42. When the gas valve 42 allows fuel to enter the burner box24, the fuel flows through a gas manifold 44 and through orifices 46 inthe manifold 44. There is one orifice 46 per burner 30. The gaseous fuelexits the orifices 46 coaxial with the longitudinal centerlines of theburners 30 at their upstream ends 30a.

The gas valve 42 also regulates a small supply of gaseous fuel to aflame ignition system to initiate combustion. To this end, a so-calledzip tube 50 supplies just enough fuel to support small flames adjacentthe downstream ends 30b of the burners 30 when ignited by a pilot burner(not shown). The pilot burner is a high energy ignitor which is alsosupplied with gaseous fuel to effect ignition.

On a call for heat, the fan 18 is energized. This causes ambient air tobe drawn into the air inlet 16, and compressed and forced into airsupply pipe 48. The air supply pipe 48 provides a flow of air into thechamber 32 through the air supply opening 34. The primary diffuser 36evenly distributes the ambient air as it passes through the primarydiffuser 36 into and along side of the burners 30. Preferably, theconfiguration of orifices in the primary diffuser 36 are arranged asillustrated in FIG. 2A. The orifice configuration is located in thecenter of the burner box opening and consists of three horizontallydisposed rows of laterally spaced orifices which are arranged in atriangular configuration. The uppermost row consists of four relativelysmall orifices 80; the middle row consists of three relatively mediumsize orifices 82; and the lowermost row consists of two relatively largeorifices 84. A portion of the advancing ambient air enters the burners30 at their upstream ends 30a. The air in the burners 30 mixes with thegaseous fuel supplied by orifices 46 by venturi action to create aprimary fuel-air mixture. The remainder of the evenly distributedambient air passes around the outside of the burners 30.

After the primary fuel-air mixture exits the burners 30 they are furthermixed with the ambient air which passed around the outside of theburners 30. The secondary diffuser 38 aids in the further mixing processto form an overall secondary fuel-air mixture. The secondary diffuserhas six equal sized orifices 86 located on the horizontal centerline ofthe burners. The six orifices direct the fuel-air mixture and mixing airtogether prior to entering the inlet of the casting flueways.

The final fuel-air mixture, composed of primary and secondary mixtures,is ignited by the small flames above the zip tubes 50 at and beyond thelocation of the secondary diffuser 38 and in the combustion chamber 40.Thus, heat is created by the burning of the final fuel-air mixture.

The important aspect of the above described burner box 24, is that aproper, pre-determined and consistent fuel-air mixture will effectefficient burning of fuel to sustain quiet, stable combustion. Thus, anefficient burner box can create and sustain higher combustiontemperatures with lower energy input. This results in lower operatingcosts, fuel conservation and less noxious gas emissions.

The Heat Exchanger

The heat exchanger 26 provides passages for the circulating fluid andthe combustion gases to transfer the heat of combustion to thecirculating fluid. To this end, the heat exchanger 26 defines a hollowcavity which receives the circulating fluid at the fluid inlet 14located on the bottom 26d of the heat exchanger 26 adjacent its rear26b. The heat exchanger 26 discharges the circulating fluid at the fluidoutlet 12 located on the front 26c of the heat exchanger 26 adjacent itstop 26a. FIG. 7 illustrates with dashed arrows the path of thecirculating fluid.

As best seen in FIG. 2, the heat exchanger 26 defines upper horizontalpassageways 54 through which the hot combustion gases enter from theburner box 24 and travel toward the rear 26b of the heat exchanger 26.The combustion gases then travel downward through a vertical passageway56 which ends adjacent to lower horizontal passageways 58. Thecombustion gases travel toward the front 26c of the heat exchanger 26through the lower horizontal passageways 58 which lead to the flue 22 toexhaust the gases to the atmosphere. FIG. 7 illustrates with solidarrows the path of the combustion gases through the heat exchanger 26.Along the entire trip, the combustion gases release heat to the heatexchanger 26 and to the circulating fluid therein by convection andradiation.

The heat exchanger 26 is of modular construction so that it can bereadily adapted to accommodate various heating system capacities. Tothis end, the heat exchanger 26 comprises a front section 60, a rearsection 62 and any number of intermediate sections 64. As illustrated inFIGS. 2 and 8, three intermediate sections 64 are used; however,depending on the specific heating system requirements, up to twentyintermediate sections 64 can be installed. All sections 60, 62 and 64are hollow and manufactured of cast iron.

The front section 60 is located adjacent a back flange 24b of the burnerbox 24; whereas, the rear section 62 is the section most remote from theburner box 24. Each of the sections 60, 62 and 64 are filled with fluidwhich can circulate therethrough.

The fluid is first received by the rear section 62 via fluid inlet 14.As seen in FIG. 6, the rear section 62 has a pair of ports 66 whichprovide passages for the fluid to circulate to the adjacent intermediatesection 64. Likewise, as shown in FIG. 5, all the intermediate sections64 have ports 66 which communicate with the adjacent intermediatesection 64, or the front section 60. Finally, the front section 60 has apair of ports 66 which receives fluid from the adjacent intermediatesection 64 and allows the fluid to exit the heat exchanger 26 throughthe fluid outlet 12.

A tight seal is created between sections 60, 62 and 64 to provide aleak-free passage of the fluid. Nipples 68 made of cast iron, or steel,are provided on the rear section 62, and on one side of the intermediatesections 64, for insertion into the mating port 66 on the adjacentsection. When the sections are compressed the leak-free seals arecreated and the heat exchanger assembly is complete. The sections remaincompressed by the use of horizontally positioned tension rods (notshown) bolted to the sides of the sections as is common in the art.

The front section 60 and the intermediate sections 64 have a pluralityof passages extending horizontally through their hollow structure toprovide a sealed path for the combustion gases. The top halves of thefront section 60 and the intermediate sections 64 each have six passages54a, one for each burner 30. When the sections are aligned andcompressed together, the passages 54a form six upper horizontalpassageways 54 for the combustion gases as they exit the burner box 24.

The rear section 62 is designed to reverse the flow of the combustiongases toward the front 26c of the heat exchanger 26. To this end, therear section 62 has a pinned surface 70 for receiving the combustiongases after exiting the upper horizontal passageways 54 and fordeflecting the flow of the combustion gases downward. The intermediatesection 64 confronting the rear section 62 also can have a pinnedsurface 88 as shown in FIG. 8.

The bottom halves of the front section 60 and the intermediate sections64 have passages 58a for receiving the flow of combustion gases afterbeing reversed by the rear section 62. As shown in the drawings, theintermediate sections 64 have three oval shaped passages 58a, while thefront section 60 has a funnel-shaped passage 58a which leads to the flue22. The flue 22 provides a path for flowing the gases out of thebuilding.

Porous cylindrical, or square, refractory blocks 74, such as reticulatedceramic, are located centrally in the upper horizontal passageways 54 inthe intermediate sections 64 to provide thermal inertia and to enhancethe transfer of heat from the combustion gases to the circulating fluid.The refractory blocks 74 are spaced from the walls of the upperhorizontal passageways 54 by fins 72. The combustion gases flow throughinternal passages in the refractory blocks 74. The internal passages inthe sponge-like structure of the refractory blocks 74 minimize thepressure drop of the flowing gases through passages 54a. The refractoryblocks 74 absorb heat.

The heat exchanger 26 of the present invention includes other conceptswhich aid in the efficient transfer of heat. For example, the passages58a in the front section 60 and the intermediate sections 64 areprovided with fins 72 which aid in conduction of heat to the circulatingfluid. The rear section 62 contains the coolest of the circulatingfluid; therefore, as the combustion gases travel downward along thevertical passageway 56 defined by the pinned surface 70 of the rearsection 62 and the pinned surface 88 of the pinned intermediate section64, further heat is removed from the gases and transferred to the fluid.The lower horizontal passageways 58 provide the final heat transfer byconvection. When the combustion gases are released outdoors, thetemperature of the combustion gases is significantly reduced to reducethe amount of noxious emissions. In addition, gaskets 76 are providedbetween adjacent sections 60, 62 and 64 and between the top and bottomhalves of sections 60 and 64, to ensure sealed passageways.

The above described heat exchanger 26 provides an extremely compactdesign which optimizes heat transfer.

In view of the foregoing, it should be apparent that the presentinvention now provides a boiler of modular construction capable of beingfitted with a selected number of heat exchange sections to suit therequirements of the specific heating system in which it is to beinstalled. The boiler provides a fuel burner assembly which is quiet,stable and fuel efficient. The boiler optimizes heat transfer so that adesirable combustion temperature can be maintained, noxious emissionscan be reduced, and efficient use of fuel can be achieved.

While a preferred embodiment of the present invention has been describedin detail, various modifications, alterations, and changes may be madewithout departing from the spirit and the scope of the present inventionas defined in the appended claims.

We claim:
 1. A boiler assembly for heating a fluid which circulatesthrough a sealed radiator/convector heating system, comprising:aplurality of burners, said burners being located in a path of flowingair such that air flows from an upstream direction through, alongsideand past said burners, said burners being directed in a downstreamdirection; means for supplying gaseous fuel to said burners; a primarydiffuser located across said path of air upstream from said burners forevenly distributing the flow of air through and alongside said burnerssuch that a primary fuel-air mixture is created inside each said burner;and a secondary diffuser located across said path of air downstream fromsaid burners for evenly mixing said primary fuel-air mixture exitingsaid burners with the air which flowed alongside said burners to createa secondary fuel-air mixture; whereby quiet, stable combustion of saidsecondary fuel-air mixture can be sustained downstream from said burnersproviding combustion gases to heat the fluid.
 2. A boiler assemblyaccording to claim 1, further comprising a burner box which houses saidburners, said primary diffuser and said secondary diffuser, said burnerbox having a combustion chamber adjacent said secondary diffuser andopposite said burners where said secondary fuel-air mixture burns.
 3. Aboiler assembly according to claim 2, further comprising a heatexchanger located adjacent said burner box for receiving the combustiongases and transferring heat from the combustion gases to the circulatingfluid, said heat exchanger having a hollow structure for fluid tocirculate therethrough, and said heat exchanger having a passagewaylocated adjacent said combustion chamber for allowing the flow of thecombustion gases therethrough, whereby heat from the combustion gases istransferred to the fluid through said hollow structure by convection andradiation.
 4. A boiler assembly according to claim 3, further comprisinga porous refractory block located in said passageway.
 5. A boilerassembly according to claim 4, wherein said heat exchanger includes arear section located downstream from said passageway, for reversing theflow of the combustion gases into a lower heat exchanger passageway. 6.A boiler assembly according to claim 5, wherein said heat exchangerincludes a front section located adjacent said combustion chamber ofsaid burner box and forming at least a part of said passageway and saidlower passageway.
 7. A boiler assembly according to claim 6, whereinsaid heat exchanger includes at least one intermediate section locatedbetween said front section and said rear section, said at least oneintermediate section forming at least a part of said passageway and saidlower passageway.
 8. A boiler assembly according to claim 7, whereinsaid passageway and said lower passageway are lined with fins to enhancethe conduction of heat.
 9. A boiler assembly according to claim 8,wherein said rear section has a pinned surface which is impinged upon bythe combustion gases.
 10. A boiler assembly according to claim 9,wherein said front section and said intermediate section have anipple-port connection to allow the fluid to circulate from saidintermediate section to said front section; and wherein said rearsection and said intermediate section have a nipple-port connection toallow the fluid to circulate from said rear section to said intermediatesection.
 11. A boiler assembly according to claim 10, wherein said rearsection has an inlet for receiving the circulating fluid, and whereinsaid front section has an outlet providing discharge of the circulatingfluid.
 12. A boiler assembly according to claim 11, wherein said frontsection and said intermediate section have gaskets therebetween so thatsaid passageway and said lower passageway are sealed tight from eachother and from a surrounding environment, and wherein said rear sectionand said intermediate section have a gasket therebetween to seal thecombustion gases from the surrounding environment.
 13. A boiler assemblyfor heating a fluid which circulates through a sealed radiator/convectorheating system, comprising:a burner box having an air chamber, aplurality of burners and a combustion gas chamber, said air chamber andsaid burners being separated by a primary diffuser, and said burners andsaid combustion gas chamber being separated by a secondary diffuser; airsupplying means for supplying ambient air to said air chamber to createa path of flowing air through said air chamber, through and around saidburners, and into said combustion gas chamber; gaseous fuel supplyingmeans for supplying gaseous fuel to said burners; said primary diffuserbeing positioned substantially perpendicular to said path of air, saidprimary diffuser having a plurality of apertures therein so that theflowing air is evenly distributed to and around said burners such that aprimary fuel-air mixture is created inside each said burner; saidsecondary diffuser being positioned substantially perpendicular to saidpath of air, said secondary diffuser having a plurality of aperturestherein to evenly mix said fuel-air mixture exiting said burners withthe air which flowed around said burners to create a secondary fuel-airmixture; and ignition means for igniting said secondary fuel-airmixture, wherein combustion takes place in said combustion gas chamberin a sustainable quiet and stable manner.
 14. A boiler assemblyaccording to claim 13, further comprising a multi-sectional heatexchanger for receiving the combustion gases from said combustion gaschamber and for transferring the heat of the combustion gases to thefluid passing through said heat exchanger.
 15. A boiler assemblyaccording to claim 14, wherein said multi-sectional heat exchangerincludes a rear section having an inlet for the circulating fluid, afront section having an outlet for the circulation fluid, and at leastone intermediate section located between said front section and saidrear section, said front, back and intermediate sections having passagesfor the flow of fluid therebetween.
 16. A boiler assembly according toclaim 15, wherein said front section is adjacent said combustion gaschamber, wherein said front and intermediate sections define an upperhorizontal passageway for the combustion gas to pass therethrough, andwherein a reticulated ceramic block is located in said upper horizontalpassageway in said intermediate sections.
 17. A boiler assemblyaccording to claim 16, wherein said upper horizontal passageway is linedwith fins to support said reticulated ceramic block.
 18. A boilerassembly according to claim 17, wherein said rear section has a pinnedsurface impinged on by the combustion gases as they exit said upperhorizontal passageway, and wherein the combustion gases traveldownwardly along said pinned surface.
 19. A boiler assembly according toclaim 18, wherein said front and intermediate sections define a lowerhorizontal passageway for receiving the flow of the combustion gasesfrom said pinned surface and discharging the combustion gases to a flue.20. A boiler assembly for heating a fluid which circulates through asealed radiator/convector heating system, comprising:at least one burnerfor burning a gaseous fuel to create hot combustion gases; amulti-sectional heat exchanger for receiving the hot combustion gasesfrom said burner and for transferring the heat of the combustion gasesto the fluid passing through said heat exchanger; said multi-sectionalheat exchanger including a rear section having an inlet for thecirculating fluid, a front section having an outlet for the circulationfluid, and at least one intermediate section located between said frontsection and said rear section, said front, back and intermediatesections having ports for the flow of fluid therebetween; and said frontand intermediate sections defining a horizontal passageway for thecombustion gases, said horizontal passageway having a plurality of finsfor supporting a refractory block within said horizontal passageway. 21.A boiler according to claim 20, further comprising a burner box havingan air chamber, a plurality of burners and a combustion gas chamber,said air chamber and said burners being separated by a primary diffuser,and said burners and said combustion gas chamber being separated by asecondary diffuser; air supplying means for supplying ambient air tosaid air chamber to create a path of flowing air through said airchamber, through and around said burners, and into said combustion gaschamber; gaseous fuel supplying means for supplying gaseous fuel to saidburners; said primary diffuser being positioned substantiallyperpendicular to said path of air, said primary diffuser having aplurality of apertures therein so that the flowing air is evenlydistributed to and around said burners such that a primary fuel-airmixture is created inside each said burner; said secondary diffuserbeing positioned substantially perpendicular to said path of air, saidsecondary diffuser having a plurality of apertures therein to evenly mixsaid primary fuel-air mixture exiting said burners with the air whichflowed around said burners to create a secondary fuel-air mixture; andignition means for igniting said fuel-air mixture; wherein combustiontakes place in said combustion gas chamber in a sustainable quiet andstable manner.